During World War II, Camille Ernst was the administrative secretary-general of the département of Herault in Montpellier, which meant that he was the unofficial head of the local gendarmerie. Nevertheless, he helped hundreds of Jews survive the war. In his postwar testimony, Rabbi Henri Schilli noted that Ernst regularly apprised Jews of impending arrests in the vicinity and issued special orders that allowed non-naturalized Jews to remain in his département. These orders undoubtedly helped the Jews survive, for otherwise, they would have been at risk of deportation. Ernst facilitated the release and rescue of hundreds of Jewish children from detention camps in southwestern France, by authorizing their move to Herault. After they arrived in Herault, the children were dispersed and accommodated in various institutions sponsored by Jewish rescue organizations with which Ernst was in contact.

Ernst's willingness to help Jews became widely known, and Jews in trouble were referred to him. Malka Shapira, who had despaired after gendarmes arrested her fiancé, was sent directly to Ernst, who arranged the release of her fiancé from his internment camp and thereby saved his life. The Vichy government discovered Ernst's activities and demanded an explanation. When he failed to account for his inefficiency in arresting Jews, he was handed over to the Germans and sent to Dachau. He survived Dachau, returned to France in 1945, his health ruined, feeling like "someone who has returned from Hell." After he recovered, he was appointed head of the departement and later became director of the political department of the French Ministry of the Interior.